Abstract

In this article, we are elaborating an example of predictive rockfall assessment by using Terrestrial Laser Scanning (TLS) in monitoring a road cut, hosted in flysch rock formation, near Ljig in Serbia. A sequence of rockfall events from 2013-2019 is presented, while the cut has been more broadly investigated in our earlier work. Beside occasional rockfalls which are routinely detected by annual TLS monitoring, it was possible to track the pre-failure deformations preceding a series of rockfalls, reaching 0.3 m3 in volume with 0.5 annual reoccurrence probability. Monitoring enabled identification of subtle displacements of about 1 cm after the first event in 2014 and keeping track of its progression. After a series of events in the following years, we were able to define the pre-failure threshold which can be applied to the adjacent rock blocks, assuming a similar block volume. It also enabled us to anticipate and simulate the event before it happens. This approach allows planning, prevention and protection, and there is a great deal of interest to standardize it for high-risk slopes and cuts in rock masses.

Introduction

Rockfalls are studied from various aspects and should be first observed from a wider, geo-structural and geomorphological context, which govern its local development. Studying of rockfalls primarily relies on historic data on their: spatial context; volume; frequency/return periods; runout and velocity. In practice, this is rarely as systematic as it should be, and data are usually scarce. Modeling and simulation is another tool that can be used to estimate some of the rockfall parameters and compensate for the lack of specific data [1]. Suspicious rock faces can be monitored for longer periods, using multiple monitoring systems (primarily Terrestrial Laser Scanning - TLS), seasonally or annually, or even in real-time. This provides systematic data for better understanding of the (pre)failure stages and allows for their linking with the triggering conditions. These precursory indicators are the subject of this research, which supports standardization of the monitoring practice in the rockfall management. One isolated rockfall example will be presented, while the entire rock slope will be analyzed in greater depth in the near future.

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